Thermo Fisher Scientific Ion Selective Electrodes Potassium - Manual (Page 4)

Instruction Manual Potassium Electrode
4
GENERAL PREPARATION
Electrode Preparation
Remove any rubber caps covering the electrode tips and the rubber inserts covering the filling holes
of the reference electrode. Fill the combination electrode or the reference electrode with the filling
solution shipped with the electrode to a level just below the fill hole. No preparation is required for
a sealed reference electrode. Gently shake the electrode downward in the same manner as a clinical
thermometer to remove any air bubbles which might be trapped behind the potassium membrane.
Prior to first usage, or after long term storage, immerse the potassium electrode in potassium
standard for thirty minutes. The electrode is now ready for use.
Connect the electrodes to the proper terminals as recommended by the meter manufacturer.
Electrode Slope Check (with pH/mV meter)
(Check electrodes each day)
1. To a 150 ml beaker, add 100 ml of distilled water and 2 ml of ISA. Place the beaker on a
magnetic stirrer and begin stirring at a constant rate. After assuring that the meter is in the
millivolt mode, lower the electrode tips into the solution. If drifting or instability is
observed, see the
TROUBLESHOOTING
section.
2.
Using a pipet, add 1 ml of 0.1M or 1,000 ppm potassium standard to the beaker. When the
reading is stable, record the mV reading.
3.
Using a pipet, add 10 ml of the same potassium standard used above to the beaker. When
the reading has stabilized, record the mV reading.
4.
Determine the difference between the two readings. The electrode is operating correctly if
the mV potential has changed by 56
±2 mV, assuming the solution temperature is between
20
o
and 25
o
C. See the
TROUBLESHOOTING
section if the potential change is not within this
range.
Slope is defined as the change in potential observed when the concentration changes by a factor of
10.
Electrode Slope Check (with ion meter)
(Check electrodes each day)
1. Prepare standard potassium solutions whose concentrations vary by tenfold. Use either the
0.1M K
+1
or the 1,000 ppm K
+1
standard stock solutions. Use the serial dilution method for
this preparation.
2.
To a 150 ml beaker, add 100 ml of the lower value standard and 2 ml of ISA. Place the
beaker on the magnetic stirrer and begin stirring at a constant rate. Lower the electrode tips
into the solution. Assure that the meter is in the concentration mode.
3.
Adjust the meter to the concentration of the standard and fix the value in the memory
according to the meter manufacturer's instructions.